There doesn't appear to be any episode tracking for titles watched on Paramount+. For example, I'm watching the first season of Star Trek Discovery and each time I get back to it there is nothing to indicate the episodes I've watched, and a 'resume watching' feature is nowhere to be found. It happens for all titles via Roku. When logging into the web via PC there is a resume function and the correct episode is identified.
There should be tracking. I have had it for a long time (when it was CBS All Access), and I have resume episode. Make certain you are using the exact same login. Hopefully, you are not subscribing through Roku, but directly with Paramount.